Transparent conducting films play an important role in many devices combining light with electrical function in a number of applications. Depending on the application (e.g., displays, touch screens, solar cells), the transparent conducting films are used to form electrodes having unique combinations of electronic, optical, and surface properties.
Transparent conductors can be important material components in commercially viable optoelectronic devices, as they combine the properties of high transmission in the visible spectral range and low sheet resistivity. Materials used for these applications should not significantly suffer from disadvantages, such as poor natural abundance, high-cost processing steps (some require high temperatures and vacuum chambers) and/or inability to bend with flexible substrates—thus making these materials difficult to implement with low-cost and high-throughput electronic applications.
In the context of photovoltaic (PV) cells, transparent conductive films are often used as both the top transparent electrode as well as the back electrode of the device stack. Texturing techniques are often employed to induce light scattering and thus increase photon path lengths and the probability of absorbing sub-band gap energy photons as well as to offset absorption losses due to the use of less photovoltaic active layer material in the cell.
Established deposition technologies involve high temperature, vacuum sputtering processes, and harsh chemicals, which can result in less-than-ideal film texturing. For example, transparent conductive films have been produced using vacuum deposition of indium tin oxide (ITO), fluorine doped tin oxide (FTO), or aluminum doped zinc oxide (Al:ZnO). These methods produce brittle films using scarce materials and/or capital-intensive techniques.
Recent developments in low-temperature, solution-processable transparent electrode replacements (using metal/semiconductor nanostructures and carbon based nanomaterials) have achieved comparable performances to ITO. However, effectively scattering light using these approaches has been challenging, which can present difficulties when trying to fabricate a scattering transparent conductive electrode for poorly absorbing thin film PVs. Further, films can be too rough to be used with organic materials (e.g., organic light emitting diodes (OLED), organic photovoltaic cells, etc.). For example, OLEDs devices are very sensitive to the roughness of the transparent conductive layer (high roughness leads to shorting between device layers).
One or more embodiments may address one or more of the above issues.